This invention relates to a fluorescent lamp assembly and, in particular, to a fluorescent lamp assembly which is compact, lighweight and efficient.
The fluorescent lamp is one of the most widely utilized light source in the world for general illumination, primarily because of its relatively low initial cost and its efficacy; i.e., its light output relative to its power input, usually expressed as lumens per watt (LPW). Nevertheless, for home use, the fluorescent lamp has not taken precedence over the incandescent lamp. Many reasons have been advanced for this lack of acceptance, among them the poor color rendition of some fluorescent lamps and their need for a ballast. However, one of the major disadvantages lies in the fact that a fluorescent lamp is a linear light source whereas an incandescent lamp can almost be considered a point source.
It is desirable to have the combination of lamp and ballast as compact, lightweight and efficient as possible.
One such lightweight ballast is disclosed in U.S. Pat. No. 3,996,493 dated Dec. 7, 1986 to Davenport et al. This patent discloses an integral self-contained fluorescent lamp unit comprising a conventional, elongated lamp and an elongated ballast resistor carried in an outwardly extending housing member positioned alongside the lamp. The use of a resistive ballast is lighter in weight and less expensive than an inductive ballast; however, the system is less efficient.
Another lightweight ballast is disclosed in U.S. Pat. No. 4,288,725 dated Sept. 8, 1981 to Morton. The Morton patent discloses a lightweight starting and operating ballasting means for starting and operating a conventional fluorescent lamp utilizing a series connected resistor and capacitor.
Fluorescent lighting systems, as mentioned above, which use purely or partly resistive ballasting both consume unnecessary power and are generally inefficient.
Capacitors, which are lightweight and consume very little power, have not been used independently to ballast to conventional fluorescent lamps. In low frequency (50-60 Hertz) a.c. current circuits, the purely capacitive ballast produces instability in the discharge and destructively high current crest factors (i.e. the ratio of the peak value of current to the average value).
Short arc length fluorescent lamps (i.e. less than about 120 mm) have been found to operate on capacitive ballasts without instability and high current crest factors. The lamp voltage upon reignition in each half cycle so the line voltage can be less than the average voltage. The voltage is not redistributed on reignition and the capacitor does not need to be charged up immediately. Consequently, there is no current spike at reignition.
The conventional short arc length, low voltage fluorescent lamps operating on a capacitor (or inductor) usually have a low efficiency, since the shorter discharge path results in relatively smaller power dissipation in the positive column.